Nos Notification Service

Building and running

Buid the program like so:

$ go build -o notification-service ./cmd/notification-service
$ ./notification-service

The program takes no arguments. There is a Dockerfile available.

Configuration

Configuration is performed using environment variables. This is also the case for the Dockerfile.

NOTIFICATIONS_NOSTR_LISTEN_ADDRESS

Listen address for the websocket connections in the format accepted by the standard library.

Optional, defaults to :8008 if empty.

NOTIFICATIONS_METRICS_LISTEN_ADDRESS

Listen address for the prometheus metrics server in the format accepted by the standard library. The metrics are exposed under path /metrics.

Optional, defaults to :8009 if empty.

NOTIFICATIONS_FIRESTORE_PROJECT_ID

Your Firestore project id.

Required.

NOTIFICATIONS_FIRESTORE_CREDENTIALS_JSON_PATH

Path to your Firestore credentials JSON file.

Required if you are not using the emulator (FIRESTORE_EMULATOR_HOST is not set).

NOTIFICATIONS_APNS_TOPIC

Topic on which APNs notifications will be sent. Probably your iOS app id.

Required.

NOTIFICATIONS_APNS_CERTIFICATE_PATH

Path to your APNs certificate file in the PKCS#12 format. They normally come in a different format I think so you need to presumably export this from your keychain.

Required.

NOTIFICATIONS_APNS_CERTIFICATE_PASSWORD

Password to your APNs certificate file.

Optional, leave empty if the certificate doesn't have a password.

NOTIFICATIONS_ENVIRONMENT

Execution environment. Affects:

• whether testing or production APNs server is used

Optional, can be set to PRODUCTION or DEVELOPMENT. Defaults to PRODUCTION.

NOTIFICATIONS_LOG_LEVEL

Log level.

Optional, can be set to TRACE, DEBUG, ERROR or DISABLED. Defaults to DEBUG.

NOTIFICATIONS_GOOGLE_PUBSUB_ENABLED

Optional, defaults to false. If set needs to be either true or false. Specifies if Google pubsub events are generated.

NOTIFICATIONS_GOOGLE_PUBSUB_PROJECT_ID

Required, project ID used for Google Cloud Pubsub. Relevant only when NOTIFICATIONS_GOOGLE_PUBSUB_ENABLED is set to true.

NOTIFICATIONS_GOOGLE_PUBSUB_CREDENTIALS_JSON_PATH

Path to your Google Cloud credentials JSON file. Relevant only when NOTIFICATIONS_GOOGLE_PUBSUB_ENABLED is set to true.

FIRESTORE_EMULATOR_HOST

Optional, this is used by the Firestore libraries and can be useful for testing but you shouldn't ever have to set this in production.

Metrics

See configuration for the address of our metrics endpoint. Many out-of-the-box Go-related metrics are available. We also have custom metrics:

• application_handler_calls_total
• application_handler_calls_duration
• relay_downloader_count
• subscription_queue_length

See service/adapters/prometheus.

Contributing

Go version

The project usually uses the latest Go version as declared by the go.mod file. You may not be able to build it using older compilers.

How to do local development

Obtaining an APNs certificate

1. Obtain a certificate from Apple (see "Obtain a provider certificate from Apple"). For development ensure that you are creating a certificate of type "Apple Push Notification Service SSL (Sanbox)" to avoid sending notifications in production.
2. Export the certificate from your keychain in the PKCS#12 format.

Run the service

You have two options when it comes to using Firestore: a local emulator using Docker or a real Firestore project that we setup for development.

Using Firestore emulator

1. Start the docker daemon.
2. Run make recreate-emulator to start the Firestore emulator using Docker compose.
3. Run the following command changing NOTIFICATIONS_APNS_CERTIFICATE_PATH and NOTIFICATIONS_APNS_CERTIFICATE_PASSWORD:

NOTIFICATIONS_APNS_CERTIFICATE_PATH="/path/to/your/apns/cert.p12" \
NOTIFICATIONS_APNS_CERTIFICATE_PASSWORD="your cert password if you set one" \
FIRESTORE_EMULATOR_HOST=localhost:8200 \
NOTIFICATIONS_FIRESTORE_PROJECT_ID=test-project-id \
NOTIFICATIONS_APNS_TOPIC=com.verse.Nos \
NOTIFICATIONS_ENVIRONMENT=DEVELOPMENT \
go run ./cmd/notification-service

Using nos-notification-service-dev project

1. Download credentials for the project. Those are your private credentials don't use them for production.
2. Run the following command changing NOTIFICATIONS_APNS_CERTIFICATE_PATH, NOTIFICATIONS_APNS_CERTIFICATE_PASSWORD and NOTIFICATIONS_FIRESTORE_CREDENTIALS_JSON_PATH:

NOTIFICATIONS_APNS_CERTIFICATE_PATH="/path/to/your/apns/cert.p12" \
NOTIFICATIONS_APNS_CERTIFICATE_PASSWORD="your cert password if you set one" \
NOTIFICATIONS_FIRESTORE_CREDENTIALS_JSON_PATH="/path/to/your/credentials/file.json" \
NOTIFICATIONS_FIRESTORE_PROJECT_ID="nos-notification-service-dev" \
NOTIFICATIONS_APNS_TOPIC=com.verse.Nos \
NOTIFICATIONS_ENVIRONMENT=DEVELOPMENT \
go run ./cmd/notification-service

Tips and tricks

Normally the program doesn't deliver the same notification multiple times. You could fix it by clearing the emulator but it is probably easier to comment out lines that look similar to this in service/app/handler_process_received_event.go:

exists, err := adapters.Events.Exists(ctx, cmd.event.Id())
if err != nil {
   return errors.Wrap(err, "error checking if event exists")
}

if exists {
   return nil
}

Makefile

We recommend reading the Makefile to discover some targets which you can execute. It can be used as a shortcut to run various useful commands.

You may have to run the following command to install a linter and a code formatter before executing certain targets:

$ make tools

If you want to check if the pipeline will pass for your commit it should be enough to run the following command:

$ make ci

It is also useful to often run just the tests during development:

$ make test

Easily format your code with the following command:

$ make fmt

Writing code

Resources which are in my opinion informative and good to read:

• Effective Go
• Go Code Review Comments
• Uber Go Style Guide

Naming tests

When naming tests which tests a specific behaviour it is recommended to follow a pattern TestNameOfType_ExpectedBehaviour. Example: TestRelayDownloader_EventsDownloadedFromRelaysArePublishedUsingPublisher .

Panicking constructors

Some constructors are prefixed with the word Must. Those constructors panic and should always be accompanied by a normal constructor which isn't prefixed with the Must and returns an error. The panicking constructors should only be used in the following cases:

• when writing tests
• when a static value has to be created e.g. MustNewHops(1) and this branch of logic in the code is covered by tests

Architecture

The notification service receives custom Nostr events which contain user's relays and APNs tokens. The notification service then uses those lists of relays associated with user's public key to get all events in which the user was tagged and to generate APNs notifications for them. When Nos receives such a notification it grabs the events from the notification service by querying it like a normal relay.

flowchart LR
    Nos --> |custom registration event| Service --> |notification| APNs --> |notification| Nos --> |request for events| Service

The best entry point to start reading the code is probably service/ports/http. There you can investigate how registration events are processed and saved in the database. You can also investigate how events are returned in response to REQ requests.

To see how events are downloaded check out Downloader as well as RelayDownloader. One tricky thing there is that we use pubsub to work around the (reasonable as it forces you to do things correctly) Firestore transaction size limit. See the chart below to understand the flow.

flowchart TB
    relay-downloader["Relay downloader"]
    in-memory-pubsub["In-memory pubsub"]
    save-received-event-handler["Save received event handler"]
    firestore["Firestore"]
    firestore-in-process-block["Firestore"]
    apns["APNs"]
    process-saved-event-handler["Process saved event handler"]

    subgraph Receive nostr event
    relay-downloader --> |received nostr event| in-memory-pubsub
    end

    subgraph Save nostr event
    in-memory-pubsub --> |received nostr event| save-received-event-handler
    save-received-event-handler --> |received nostr event| firestore
    save-received-event-handler --> |`nostr event saved` pubsub event| firestore
    end

    subgraph Process nostr event
    firestore --> |`nostr event saved` pubsub event| process-saved-event-handler
    process-saved-event-handler --> |many nostr event tags| firestore-in-process-block
    process-saved-event-handler --> |many notifications| apns
    process-saved-event-handler --> |many notifications| firestore-in-process-block
    end

Deployment

We deploy this service using ansible. The steps for deployment can be read in our internal notion page.